Two arms system

ABSTRACT

Unit cranes consist of three hinged arms ( 13-15 ), the middle arm ( 14 ) being in the form of a polygon comprising a number of units jointed together, the flexibility of the units being arranged by influencing the units internally. The object of the invention is to achieve improved traction curves and speed curves, and this is effected by influencing the movement of the units from the outside by means of a hydraulic mechanism ( 38 ).

FIELD OF THE INVENTION

The present invention is directed to a two arms system, and morespecifically, toward an improved two arms system for a unit crane.

BACKGROUND OF THE INVENTION

There is a considerable call for a two-armed system for unit cranes, forinstance. Such a crane consists of a rigid arm and thereafter an armcomposed of a number of part-arms joined together which can beinfluenced hydraulically in such a manner that the part-arms form apolygon. This arm is in turn attached to a stand or to said stand via asupporting arm. The two arms in the system, together with a supportingarm if used, can thus be arranged to be situated one above the other andalso so that all the arms are extended. Various units can be attached atthe tip of the rigid arm, for use in clearing trees and bushes. Unitsfunctioning as excavators or loading means can also be attached, or evena concrete pump or concrete hose. In existing systems with two arms, thearm able to form a polygon is influenced by a hydraulic unit arrangedbetween the arm parts so that, when the polygon is extended, the unit islocated substantially in the middle of the polygon. Certain problemshave been found to occur when operating such two-armed systems, asregards speed control of the top of the rigid arm, and problems alsooccur as regards the force exerted at said tip. Such a unit crane issuitable fitted on a caterpillar vehicle and this involves the problemof how to fold up the crane when it is not in operation. The arms willusually have a substantially vertical position, or they will be situatedon the roof of the vehicle. There is also the problem of the actualjoints of the unit arms being as stable as possible.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above-mentioneddrawbacks and this is achieved by it being possible for both the arms inthe system to be caused to lie one above the other, and possible alsoabove a supporting arm so that, when the arm system is not in use thefree end of the arm with several parts is attached either to a stand orto one end of a supporting arm, the other end of which is journalled inthe stand. When folded up, therefore, the actual working tip or cranetip of the journalled package will be situated at the opposite part ofthe stand. To achieve suitable lifting power and suitable speed thecrane tip is moved from a packaged position to the position is assumeswhen the tip is furthest away from the stand. The hydraulic mechanisminfluencing the arm with the many parts is arranged so that itinfluences two points situated outside two adjacent arm parts.

According to a preferred embodiment of the invention it is suitable touse a supporting arm which is in connection with a stand. In this caseit is advisable to use two pairs of hydraulic cylinders. One pair ofhydraulic cylinders is connected to the stand and to a point between theends of the supporting arm. The supporting arm can be caused to moveabout its journalling point by means of one of the hydraulic cylinders.At the point between the two ends of the supporting arm it is suitableto arrange a bearing for a pair of hydraulic cylinders, one end of whichis connected to said journalling point and the other end of whichcommunicates with one end of the arm that can form a polygon. The firstpair of hydraulic cylinders is used so that one hydraulic cylinder ofthe pair controls the movement of the supporting arm while the otherhydraulic cylinder, together with the second pair of hydrauliccylinders, forms a closed hydraulic system, and since the secondhydraulic cylinder in the first pair is parallel with the hydrauliccylinder infulencing the movement of the supporting arm, the secondhydraulic cylinder in the first pair will automatically control themovement of the two hydraulic cylinders influencing the arm able to forma polygon. This arrangement of hydraulic cylinders provides smoothermovements of the whole crane, as well as enabling savings in energy.

The stand to which the supporting arm is attached can be caused to movedin a number of different ways known per se. However, it has provedparticularly advantageous if the stand is provided at its journallingend with one or more toothed wheel rims situated one above the other,each cooperating with a chain designed for cooperation with a toothedwheel, each chain being joined at its ends and the chains beinginfluenced by a hydraulic system so that the chains are caused to moveand influence the pin of the stand in order to effect movement of thestand.

The arrangement described above with toothed wheel and chain allows thecrane to be moved as large an angle as possible in both direction.However, if the demand for a large turning angle is not so great, it ismuch simpler and less expensive to use two links joined together foreach piston rod.

Such a unit crane with its stand is suitable arranged on a platformprovided with cab in such a way that the arm system in the form of apackage does not come into contact with the cab in any way. The vehiclecarrying the crane package may be part of a centrally controlled vehiclein which the engine is jointed to the supporting part for the cranepackage. By arranging the hydraulic unit outside the arm with the manypart arms, the advantage is gained that the crane can be brought to bemore or less horizontal with the various arms arranged one after theother and that it can be caused to assume a substantiallydownwardly-directed vertical position and upwardly-directed verticalposition. The many joints in the arm system are subjected toconsiderable strain and it is therefore suitable for two arms to becombined so that one arm has two parallel shafts between which a pinlocated on the other arm is passed. The pin and the two arms togetherform a through-hole for a shaft journal. Each end of the shaft journalis provided with a tensioning ring having a conical surface and atensioning cone, also having a conical surface, cooperating therewith.These two units with conical surfaces are brought into rigid contactwith each other since the end cone is provided with a tightening boltthat can be screw into each end of the shaft journal. Reliablefunctioning of the shaft journal located at a point about which the twoarms can be oscillated is thus achieved.

Additional characteristics of the present invention are revealed in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail withreference to the accompanying drawings in which

FIG. 1 shows a centrally controlled vehicle with a crane package in restposition, the vehicle being on its way to a work place,

FIG. 2 shows the vehicle at a work place where the unit crane ismanipulating a tree,

FIG. 3 shows a unit crane and stand in partially extended position.

FIGS. 4-6 show various positions of a unit crane,

FIG. 7 shows an arrangement for retaining shaft journals at a joint,

FIG. 8 shows how the force in a crane tip varies between two possiblepositions of the crane tip,

FIG. 9 shows how the speed of the crane tip varies between its twooutermost positions,

FIG. 10 shows a modification of the hydraulic system at the supportingarm according to FIG. 3,

FIG. 11 shows a flow chart for the hydraulics for the pistons accordingto FIG. 10,

FIG. 12 shows schematically a section of the turning device for thestand according to FIG. 3,

FIG. 13 shows a section along the line 22 in FIG. 1,

FIG. 14 shows a schematic section through a chain wheel,

FIG. 15 shows a detail according to the arrangement in FIG. 12,

FIG. 16 shows a modification of the arrangement according to FIG. 12,

FIG. 17 shows a modification of the pivoting arrangement utilizinglinks,

FIG. 18 shows an arrangement according to FIG. 17, seen from above, and

FIG. 19 shows only the links according to FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 11 designates a centrally controlled vehicle with a unit crane.The vehicle has an engine part arranged pivotably in relation to thesupport unit 3 for a crane unit. The engine part has a pair of frontwheels and the support part 3 has bogie wheels 5. A cab 6 is arranged onthe support part. This cab may be pivotable depending on which directionthe vehicle is to be driven in. Naturally the cab may also be stationaryand control means may be arranged in the cab so that the operator needonly turn his seat 180°. A stand is arranged on the supporting unit,said stand being pivotably arranged by means of bearings 11, themovement of the stand being achieved with the aid of hydraulic cylinders12. The complete crane package consisting of three arms has beendesignated 8. Considering now the centrally controlled vehicle 1 in FIG.2, this is shown in operation and it can be clearly seen that the armpackage has a two-armed system 9 and also a supporting arm 13. Thetwo-armed system is shown manipulating an object 10, which in thepresent case is a tree, and the operation shown comprises the vehiclewith the crane package attempting to exert pressure on the tree.

FIG. 3 shows the crane package with stand in partially extendedposition. It can be seen that the inner arm 14 in the two-armed systemis journalled at one end to a rigid arm 15 with a crane tip 16. Theinner arm 14 is journalled at its inner end on a supporting arm 13 whichis in turn journalled on the stand 7. The inner arm 14 consists of afirst arm 17, a second arm 18, a third arm 19 and a fourth arm 20. Alljournalling points 22-34 joining the various parts of the arms togethermay be of the same type. One end of an arm part consists of two shaftparts and the connecting arm part consists of a studlike part which isplaced between the two parts, the two parts and the stud part havingholes that form a common hole for a shaft journal and this shaft journalis anchored in a special manner to be described in the following. Thejournalling points 22-34 thus constitute joint points for the units inthe unit crane. The rear arm 14 in the crane has an arm 19 a that issubstantially solid and is provided at its end with two parallel armswith a part 19 b forming a part of the actual rear arm, whereas the part19 c is completely protruding. The fourth arm also consists of twoparallel parts spaced from each other, and has a part 20 a included inthe rear arm 14 and a part 20 b that protrudes outside the rear arm 14.Two intermediate arms are journalled at their free ends, between themiddle of the second arm 18 and the upper end of the arm 19 a. The lowerend of the stand 7 comprises a plate, pivotable in relation to asubstantially parallelepipedic part 35 which is turnable about ahorizontal axis by means of hydraulic cylinders 12 shown in FIG. 1.Above the pivotable plate 37 the stand 7 is provided with two flanges36. Between the two journalling points 28 and 30 are two hydrauliccylinders that influence the relative movement between the two arms inthe two-armed system. At the middle of the supporting arm 13 is a flangearrangement with two journalling points 31 and 32. A hydraulicarrangement 39 is situated between the journalling points 27 and 32, anda hydraulic arrangement 40 is similarly arranged between the journallingpoints 31 and 33. The relative position between the two arms 14 and 15in the two-armed system is controlled by the hydraulic arrangement 38.The two-armed system is in turn also influenced by the hydrauliccylinder arrangement 39 and the hydraulic cylinder arrangement 40situated between the journalling points 31 and 33 controls the positionof the supporting arm 13 which also has another influence, as alreadymentioned, namely that the position of the parallelepipedic unit 35 isinfluenced by the hydraulic arrangement 12.

FIGS. 4, 5 and 6 demonstrate how the three arms in the crane package canbe brought to three extreme outermost positions. FIG. 4 shows a purelyhorizontal position, FIG. 5 directed vertical downwards and FIG. 6directed vertically upwards.

FIG. 7 shows how two arm ends can be joined together. In this case, onearm end must comprise two shafts or lugs 41 and 42 situated oppositeeach other and spaced apart. Each of the two shafts 41 and 42 isprovided with a hole 43 and 44. A solid stud 50 arranged at the end ofthe arm to be connected is inserted between the two shafts. This stud orjournal is provided with a through-opening 49. When the two arm ends arebrought into engagement with each other, the openings 43, 44 and 49 willbe situated opposite each other and a shaft journal 52 is insertedthrough them. A tensioning ring with an inner conical surface is appliedat each end of the shaft journal and is placed in the holes 34 and 44. Atensioning cone 46 with a bottom and a cylindrical wall, conical on theoutside, is applied at each end of the shaft journal 52. The conicalsurface of the tensioning cone 46 is brought into contact with theconical surface of the tensioning ring 45. In the bottom of thetensioning cone is an opening for a tightening bolt, threaded forengagement with an opening, also with threading, in the shaft journal.The two conical surfaces can thus be brought into firm contact with eachother so that the shaft journal is immovable in the two outer holes 43and 44. The shaft journal 52 may be provided with a grease cup 51 sothat the bearing can be provided internally with lubricant. The bearingarrangement described can be used in all bearing arrangements in theunit crane or just in certain selected bearings, but it should beobvious that the bearing according to FIG. 7 is generally usable and mayhave applications entirely different from vehicles with unit cranes.

The crane tip in the unit crane has two outermost positions, one asshown in FIG. 1 and the other as shown in FIG. 4. Between these twoextreme positions the curves in FIG. 8 have been taken up for forcesoperating on the crane tip, the curve 54 showing how the force variesfrom the inner position in FIG. 1 to the outer position in FIG. 4. Curve55 also shows how the force varies in an inward movement. Curve 53 inFIG. 9, finally, shows the speed of the crane tip from the situationaccording to FIG. 1 to that according to FIG. 4 and curve 52 shows theequivalent speed during an inward movement. It is thus clear that thepresent invention has managed to produce a vehicle with a unit cranewhere, when not in use, the crane forms a convenient package,substantially horizontal, and is at a low level when the three arms arearranged one after the other, which is an advantage since the crane isthen easy to service. It may then be suitable to bring the crane intothe position shown in FIG. 4. Another advantage is that the crane willon no account come into contact with the driver's cab 6. No specialvehicle is necessary as previously to transport the unit crane, andcrane and vehicle provide an advantageous unit through the use of acentrally controlled vehicle.

It is clear that the speed and lifting capacity of the crane tip 16 varydepending on the hydraulic pressure used.

The embodiment shown in FIGS. 12-16 comprises a housing 71 in which ashaft 72 is pivotably journalled, the outward end 73 of which isdesigned for mounting of the tool or unit which the pivoting arrangementis designed to handle. In the example shown the shaft 72 is providedwith two chain wheels 74 which are firmly secured to the shaft.

The housing 71 is also provided with a first cylinder 75 and a secondcylinder 76, the axes of these cylinders being parallel. A first pistonrod 77 connected to a piston is displaceably arranged in a firstcylinder 75 and a second piston rod 78 connected to a piston isdisplaceably arranged in the second cylinder 76. The first piston rod 77is provided at its free end with a first chain wheel 79 and the secondpiston rod 78 is provided with a second chain wheel 80. The chain wheels79 and 80 are freely pivotable in the ends of respective piston rods 77,78 about shafts parallel to the shaft 72.

The arrangement is symmetrical and the piston rods 77, 78 with chainwheels 79, 80 are identical. Only the piston rod 77 with chain wheel 79will therefore be described in connection with FIG. 14. The piston rod77 is provided with a through-hole 81 in which a bearing sleeve 82 isjournalled. In the example shown two chain wheels 79 are rotatablyarranged on the bearing sleeve 82, and the piston rod forms a spacerbetween the chain wheels 79. On each side of the bearing sleeve 82 alock and guide washer 83 is retained by its shaft 84 being inserted intothe cavity in the bearing sleeve 82. The side of the washer 83 facingthe bearing sleeve and chain wheel is flat and holds the chain wheel inplace axially, while the end of the washer 83 facing away from thesleeve 82 has a guiding protrusion 85, semi-circular when seen insection, which has a certain axial extension as can be seen in FIG. 15.In the example shown the guiding protrusion extends across the diameterof the washer 83 and runs in groove 86, also semi-circular when seen insection, in the opposing walls 87 of the housing 71. The washers 83,bearing sleeve 82, chain wheel 79 and end of the piston rod 77 are thusaxially “locked” between the walls of the housing 71. At the same timethe grooves 86 and the guiding protrusions 85 running therein guide theend of the piston rod 77 linearly in the housing. As can be seen in FIG.12, the piston connected to each piston rod 77, 78 has a partiallyspherical surface which cooperates with the cylinder 75, 76 and, in theexample shown, is provided with a sealing ring 88. The pistons can bedisplaced in the cylinders via hydraulic or pneumatic channels 89.

Two long, flexible members for transmitting movement, e.g. in the formof two roller chains 90, only one of which is visible in FIG. 12, aresecured to the housing 71 by their ends 91. Each chain passes 180°around the first chain wheel 79, continues 180° around the chain wheel74 and then 180° around the second chain wheel 80. Chain guides 92 areprovided at the attachment of the chain ends 91 to the housing 71 toguide and support the end portions of the chain. The first piston rod 77with its piston and the second piston rod 78 with its piston aresupplied with pressure fluid so that they move synchronously to and frombut in opposite directions i.e. when the first piston rod 77 with itspiston is in its uppermost position, as shown in FIG. 12, the secondpiston rod 78 with its piston is in its lowermost position.

It should be obvious that when the pistons and the piston rods 77 and 78move synchronously in opposite directions, the chain running around thechain wheel 74 will move, thereby turning the shaft 72. How far thechain wheel 74, and thus the shaft 72, can be turned depends naturallyon the length of the chain and the stroke length of the piston rods.However, for normal requirements a turning angle of 180° is sufficientfor the shaft 72.

Since the pistons are constantly loaded with pressure fluid, the chains90 remain taut and the arrangement is thus play-free. Since the chainsencompass the chain wheel 74 along half of its circumference, as well asthe first and second chain wheels 79 and 80, the surface pressure on thewheels will be reduced when the shaft 72 is loaded. The arrangement canthus have small dimensions while still being able to take upconsiderable loads.

FIG. 16 shows a modified form of the invention, the cylinders 75 and 76having been mounted at 90° to each other. The function is the same asdescribed with reference to the embodiment shown in FIGS. 12-15. In theembodiment according to FIG. 16 the chain will encompass an angle of270° of the chain wheel 74 by the shaft 72, thereby further distributingthe load on the toothed wheel 74. For reasons of clarity the grooves 86mentioned in connection with the description of FIGS. 12-16 have beenomitted but may of course be included in this embodiment also. Thegrooves will then cross each other which does not, however, affect thefunction of the pistons and guide protrusions 15, the latter havingelongate form as mentioned.

It is implicit that the wheels 79 and 80 do not necessarily have to beprovided with teeth but may have some other peripheral surface dependingon the type of chain. Cogged belts are also possible.

The arrangement described above for turning the stand with the aid oftoothed wheel and chain is suitable if large turning angles are requiredfor the unit crane. However, if such large turning angles are notnecessary then it is both cheaper and simpler to use a link systeminstead of toothed wheel and chain. FIGS. 17 and 18 show in perspectiveand seen from above a turning arrangement which is simple andinexpensive to manufacture and which uses links instead of the chainsand toothed wheels mentioned above. In most cases at least one or twopiston rods are required to achieve turning in both directions, and inthe present case the actual housing, designated 94, for the turningarrangement is shown. The pin or unit to effect turning of the stand isthen designated 13 and is in the form of a substantially cylindricalunit journalled at its ends in some suitable manner. The link and pistonarrangement of the cylindrical pin is arranged in a plane perpendicularto the central axis of the pin. A radially outwardly directed flange 100is arranged in some way on the envelope surface of the cylindrical unit.On said flange are two journalling pints for two groups of links andpiston rods. Obviously only one piston rod and two links are required toachieve turning movement in both directions but it is more advantageousto have two groups of links and pistons, the groups directed indifferent directions around the periphery of the unit. One group isconnected at the flange 100 and a link 97 is provided here which ispivotable connected by one end 104 to the outwardly directed flange 100.The other end 98 is connected to the piston rod 95. A link 101, moveablevia its end 102, is arranged between the two ends of the link 97. Theother end 103 of the link 101 is journalled at a fixed point in thehousing, arranged at a unit 104. It is thus only the end 103 that ismoveable around a stationary point. The moveable parts are thus the linkarms, piston rods and unit 93. Relatively large turning angles can beachieved in both directions thanks to the links being arc shaped. It hasproved advisable to have two levels of identical links with a spacerbetween these levels arranged at one end 98 of the link 97 andcorresponding ends for the other group with links and piston rods. It isadvantageous to have two similar types of link systems arranged oneabove the outer as this enables a better point of application with thepiston rods at the links in the different levels.

FIG. 10 shows a variation of the supporting arm 13 in FIG. 3 where thehydraulic pistons 39 and 40 have been replaced with a first pair ofhydraulic pistons 57 and 56 and a second pair of hydraulic pistons 58and 59. The hydraulic pistons 56 and 57 replace the hydraulic piston 39in FIG. 3 and these hydraulic pistons are journalled at their ends inthe same way as the hydraulic piston 39. The hydraulic piston 40according to FIG. 3 has been replaced in FIG. 10 with the hydraulicpistons 58 and 59. The hydraulic pistons in each pair are always locatedparallel to each other. The hydraulic pistons 56, 57 and 59 arehydraulically connected together in a closed system, whereas thehydraulic piston 58 is controlled by a control unit 71. The control unit71 is connected hydraulically to the hydraulic cylinder 58 by the tubes61 and 62, forming a closed hydraulic system, and controls the pistonbetween its two ends, thereby raising and lowering the supporting arm 13in relation to the post 60. Since the two pistons 58 and 59 are parallelto each other, the piston 59 will always follow the movement of thepiston 58. The pistons 59, 56 and 57 are connected by tubes 63-70 toform a closed hydraulic system which means that when the piston 58 iscaused to move by the control unit, the piston 59 will automaticallymove the pistons 56 and 57. Allowing the arm system to be influenced viathe supporting arm 13 by two hydraulically closed system reduces thetotal kinetic energy required for the unit crane.

What is claimed is:
 1. A system comprising a first rigid arm and asecond arm connected to said first arm, said second arm comprising aplurality of arm segments hingedly interconnected to form a polygon,said plurality of arm segments comprising: a first arm segment; a secondare segment having first and second ends; a third arm segment comprisinga linear portion and a base portion having first and second ends, saidlinear portion being connected to said base portion at a point betweensaid first and second ends, said base portion second end extendingoutside the polygon formed by said plurality of arm segments; a fourtharm segment having first and second ends, said third arm segment baseportion first end being connected to said fourth arm segment at a pointbetween said fourth arm segment first end and said fourth arm segmentsecond end and said fourth arm segment second end extending outside thepolygon formed by said plurality of arm segments; at least one rodconnected between the linear portion of said third arm segment and apoint on said second arm segment between said second arm segment firstend and said second arm segment second end; and, hydraulic actuatormeans connected between said third arm segment base portion second endand said fourth arm segment second end.
 2. The system of claim 1 furtherincluding a third arm having a first end connected to said second armand a second end connected to a pivotable and tiltable support.
 3. Thesystem of claim 2 wherein said third arm includes a protrusion betweensaid third arm first end and said third arm second end, a secondhydraulic actuator means connected between said protrusion and saidfourth arm segment second end and a third hydraulic actuator meansconnected between said protrusion and said support wherein one of saidsecond and said third hydraulic actuator means is controlled by theother of said second and third hydraulic actuator means.
 4. The systemof claim 2 wherein each of said second and said third hydraulic actuatormeans comprises a pair of hydraulic actuators, each of said pair ahydraulic actuators further comprising a piston mounted within acylinder and wherein a first one of the pistons of said second hydraulicactuator means pair of hydraulic actuators and said first and secondpistons of said third hydraulic actuator means pair of hydraulicactuators form a closed system, the position of the pistons of saidthird hydraulic actuator means pair of hydraulic actuators beingcontrolled by said second one of the pistons of said second pair ofhydraulic actuators.
 5. The system of claim 2 wherein said third arm ismoveable in the direction of a pivot axis of said stand.
 6. The systemof claim 2 wherein said second arm is shiftable between a first positionand a second position relative to said third arm.
 7. The system of claim2 wherein said first arm, second arm and third arm are shiftable betweena first position wherein said first arm is located on a first side ofsaid second arm and said third arm is located on a second side of saidsecond arm opposite said first side and a second position wherein saidfirst arm, said second arm and said third arm are arranged in a line. 8.The system of claim 2 including a movable vehicle, said supporting beingmounted on said vehicle.
 9. The system of claim 8 wherein said vehicleincludes bogie wheels.
 10. The system of claim 8 wherein said vehicleincludes a movable cab portion.
 11. The system of claim 8 wherein saidvehicle includes a cab portion and a second portion and an enginemounted on said second portion.
 12. The system of claim 2 wherein saidfirst rigid arm includes a free end and said free end has an arc-shapedspeed curve.
 13. The system of claim 2 wherein said first rigid armincludes a free end and said free end has greatest tractive force atfirst and second end positions and wherein an arc shaped curve definesthe tractive force between said first and second end positions.
 14. Thesystem of claim 2 wherein said connection between said interconnectedarm segments comprises a conical recess on one of said plurality of armsegments and a conical journal on another of said plurality of armsegments.
 15. The system of claim 2 wherein said first end of said baseportion of said third arm segment includes first and second opposedshafts each having a bore, said first end of said third arm includes astud having a first and second ends adapted to fit into said bore ofsaid first and second opposed shafts and a central bore, and a shaftjournal insertable through said opposed shafts and said central bore toconnect said third arm to said third arm segment.
 16. The system ofclaim 15 wherein said shaft journal includes first and second ends andeach of said first and second ends of said shaft journal includes atensioning ring.
 17. The system of claim 2 wherein said pivotablesupport includes a depending shaft supporting a toothed wheel and adrive for rotating said shaft to pivot said support, said drivecomprising a housing, first and second movable pistons havinglongitudinal axes mounted in said housing; first and second gear wheelsrotatably mounted on each of said first and second movable pistons; and,at least one long, flexible member having first and second ends securedwithin said housing on opposite sides of and in engagement with thetoothed wheel and said first and second gear wheels.
 18. The system ofclaim 17 wherein said first and second gear wheels include centralsupport shafts having end members and wherein said end members engageopenings in said housing.
 19. The system of claim 45 wherein said endmembers comprise a washer having an outwardly directed protrusionengaging in a groove in the wall of the housing, said groove runningparallel to the axes of said first and second pistons.
 20. The system ofclaim 46 wherein the axes of the pistons are substantially parallel andwherein said flexible member encircles at least 180 degrees of saidtoothed wheel.
 21. The system of claim 17 wherein said longitudinal axesare substantially perpendicular.
 22. The system of claim 17 wherein saidflexible member comprises a chain.
 23. The system of claim 17 whereinsaid flexible member comprises a cogged belt.
 24. The system of claim 17wherein said drive comprises a cylinder connected to said shaft, atleast one arc shaped link connected to a surface of said cylinder and apiston connected to each of said at least one link, whereby moving saidpiston linearly causes the rotation of said cylinder.
 25. The system ofclaim 24 wherein said at least one link comprises two links.